A wireless data terminal device is a data device capable of getting access to the Internet by using a wireless network connection, such as 3G network data card and Wireless Fidelity/Worldwide Interoperability for Microwave Access (WIFI/WIMAX) data card. In recent years, with an increasing requirement from people on electronic products, factors of the data card such as size, power consumption and speed are improved continuously to meet the market requirement. For example, a data card is improved to have a movable structure from the prior fixed structure. Such an improvement enables a computer connector or an antenna of the data card to be contracted into the data card when not in use, thereby substantially reducing the size of the data card and eliminating the influences of easily lost accessories such as a USB cap on the data card.
Because the data card is a wireless data terminal device, the radio performance is one of the important factors for measuring the performance of the data card, while the effect of connection of the data card with a computer has important influence on the radio performance of the data card. At the present time, a USB bus is a mainstream mode for establishing connection between the data card and the computer, while the fact that the connector for connecting the data card with a USB connector of the computer is changed to be in a movable type from a fixed type left great influence on the radio performance of the data card.
The inventors of the disclosure find that the existing technology has the following problems in the process of implementing the present disclosure.
In a data card with a fixed USB connector, a USB plug is directly soldered on a main circuit board of the data card. Due to the reliable connection of the USB plug with the main circuit board, it is possible that the grounding plane of a data card circuit is reliably connected with that of the computer, thereby not influencing the radio performance of the data card greatly. However, due to the limitation of size and layout of the USB connector, the data card with the fixed USB connector cannot be reduced unlimitedly, and a USB cap is required to protect the USB connector when the data card is not in use, thereby inevitably influencing the data card due to the loss of the USB cap.
By adopting the mode of separating the main circuit board of the data card from the USB connector, a movable USB connector is realized by connecting the USB connector with the main circuit board via a single thin wire or a Flexible Printed Circuit (FPC) flexible board. However, such a data card with a movable USB connector has some defects: on the one hand, due to the limitation of size of the data card and flex life of a connecting material, it is impossible to use a large connecting wire or FPC flexible board for connecting the USB connector with the main circuit board, so there is only a narrow grounding circuit, thereby the grounding plane of the main circuit board of the data card cannot be connected with that of the computer effectively; on the other hand, the poor connection effect of the grounding plane also influences the radio performance of the data card directly.
FIG. 1 is a schematic illustrating operation of an antenna. It can be known from fundamental principles of the antenna that the antenna serves to convert electric energy into an alternating electromagnetic field and radiate it to space. Under the action of the alternating electromagnetic field, there forms an electric field directing the antenna on the grounding plane surrounding the antenna, as shown in FIG. 1. The grounding plane of the antenna has one important function of enabling as much energy as possible to return to the antenna through the electric field surrounding the antenna to compensate for the energy radiated by the antenna.
When the antenna of the wireless data terminal device is in progress, the grounding plane of the wireless data terminal device serves as a part of the antenna, playing the role of returning energy. Moreover, the grounding plane of the wireless data terminal device is not able to support the energy return of the antenna due to the reduced size of the present wireless data terminal device, for example, the size of such products as a data card has tended to reach a limit. What has been done at present is to utilize the grounding planes of other devices, such as the grounding plane of the computer to support the operation of the antenna of the wireless data terminal device. Therefore, the connection of the wireless data terminal device with the grounding plane of other devices becomes very important.
Before the emergence of a wireless data terminal device with a detachable USB connector, the wireless data terminal device is connected with the computer by means of a fixed USB connector. Such a fixed USB connector is directly connected to the grounding plane of the wireless data terminal device, and is directly connected to the grounding plane of the computer side. The bonding face of the grounding plane of the fixed USB connector is large enough to enable the wireless data terminal device to well realize the return of energy by means of the grounding plane of the computer. However, the greatest problem with the wireless data terminal device with a detachable USB connector is that the USB connector is separated from the main circuit board, and can be connected to the main circuit board only by a flexible connection mode. That is, the USB connector is connected with the grounding plane of the wireless data terminal device only by a thin and narrow conductor such as a flexible wire or FPC flexible board. The requirement on the energy return of the antenna cannot be satisfied unless the flexible connection is sufficiently wide. However, the flexible connection is constrained by factors such as materials, device space, and layout and service life, thereby being difficult to be wider. Therefore, it is difficult for the radio performance of the wireless data terminal device with a detachable USB connector to satisfy the requirement when the wireless data terminal device has only one ground circuit connecting the USB connector and the grounding plane. Moreover, the ground connection further takes on return of the working current of the device, with various serious disturbances, which further deteriorates the work environment of the antenna.